U.S. patent number 8,105,675 [Application Number 12/204,584] was granted by the patent office on 2012-01-31 for honeycomb structure and bonding material to be used for same.
This patent grant is currently assigned to NGK Adrec Co., Ltd., NGK Insulators, Ltd.. Invention is credited to Tetsuhiro Honjo, Shuichi Ichikawa, Naoshi Masukawa, Atsushi Watanabe, Osamu Yamakawa.
United States Patent |
8,105,675 |
Masukawa , et al. |
January 31, 2012 |
Honeycomb structure and bonding material to be used for same
Abstract
There is disclosed a honeycomb structure 1 which is made of a
ceramic material and in which a plurality of honeycomb segments 12
having cell structures 5 and porous outer walls 7 on outer
peripheries of the cell structures 5 are integrated by bonding the
outer walls 7 to one another with a bonding material, each of the
cell structures being provided with a plurality of cells 3
constituting fluid channels divided by porous partition walls 2,
wherein the bonding material contains a bio-soluble fiber. The
honeycomb structure 1 of the present invention has a performance
equivalent to that of a honeycomb structure in which a heretofore
used ceramic fiber is contained.
Inventors: |
Masukawa; Naoshi (Kitanagoya,
JP), Watanabe; Atsushi (Nagoya, JP),
Ichikawa; Shuichi (Handa, JP), Yamakawa; Osamu
(Kani, JP), Honjo; Tetsuhiro (Kani, JP) |
Assignee: |
NGK Insulators, Ltd. (Nagoya,
JP)
NGK Adrec Co., Ltd. (Kani, JP)
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Family
ID: |
38609199 |
Appl.
No.: |
12/204,584 |
Filed: |
September 4, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090011178 A1 |
Jan 8, 2009 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2007/055457 |
Mar 16, 2007 |
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Foreign Application Priority Data
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Mar 17, 2006 [JP] |
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2006-073817 |
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Current U.S.
Class: |
428/116;
156/89.22; 501/95.1; 501/36 |
Current CPC
Class: |
C04B
35/117 (20130101); C04B 35/6316 (20130101); C04B
35/565 (20130101); B01D 46/2466 (20130101); C04B
38/0006 (20130101); C04B 35/6303 (20130101); C04B
35/80 (20130101); B01D 39/2075 (20130101); C04B
28/24 (20130101); C04B 38/0019 (20130101); B01J
35/04 (20130101); B01D 46/2448 (20130101); C04B
37/005 (20130101); C04B 28/24 (20130101); C04B
14/043 (20130101); C04B 14/303 (20130101); C04B
14/324 (20130101); C04B 14/328 (20130101); C04B
14/4643 (20130101); C04B 24/383 (20130101); C04B
38/08 (20130101); C04B 38/0019 (20130101); C04B
35/565 (20130101); C04B 35/80 (20130101); C04B
38/0054 (20130101); C04B 38/0074 (20130101); C04B
38/0645 (20130101); C04B 2235/77 (20130101); C04B
2235/5224 (20130101); B01D 46/24491 (20210801); C04B
2235/349 (20130101); C04B 2237/365 (20130101); B01D
46/2459 (20130101); C04B 2235/5436 (20130101); C04B
2235/3826 (20130101); B01D 46/2444 (20130101); Y10T
428/24149 (20150115); B01D 2239/08 (20130101); C04B
2235/526 (20130101); C04B 2237/064 (20130101); C04B
2237/083 (20130101); C04B 2235/428 (20130101); B01D
46/2425 (20130101); C04B 2111/00793 (20130101); C04B
2235/5232 (20130101); C04B 2235/5228 (20130101); C04B
2235/3418 (20130101); C04B 2235/96 (20130101); C04B
2235/5264 (20130101); C04B 2237/708 (20130101); C04B
2235/9607 (20130101); C04B 2111/0081 (20130101) |
Current International
Class: |
B32B
3/12 (20060101); C03C 13/06 (20060101); C04B
35/00 (20060101); C04B 37/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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B2-61-51240 |
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Nov 1986 |
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JP |
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A-08-506561 |
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Jul 1996 |
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JP |
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B2-3121497 |
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Oct 2000 |
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JP |
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2003-105662 |
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Apr 2003 |
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JP |
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A-2005-154202 |
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Jun 2005 |
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JP |
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WO 94/15883 |
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Jul 1994 |
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WO |
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WO 03/067041 |
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Aug 2003 |
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WO |
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Other References
Shabanova et al. "Aggregation Stability of Colloidal Silica
Sol-Polystyrene Latex Mixtures," Colloid Journal, vol. 63, No. 5,
pp. 649-652, 2001. cited by other .
Supplementary European Search Report issued on Mar. 10, 2010 in
European Patent Application No. 07738902.1. cited by other .
Gulati, Suresh T. "Strength and Thermal Shock Resistance of
Segmented Wall-Flow Diesel Filters" Corning Class Works, NY.
(1986). cited by other.
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Primary Examiner: Baldwin; Gordon R
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
The invention claimed is:
1. A honeycomb structure made of a ceramics, consisting of a
plurality of honeycomb segments provided with cell structures
having a plurality of cells constituting fluid channels divided by
porous partition walls and porous outer walls on outer peripheries
of the cell structures, and integrated by bonding the outer walls
to one another with a bonding material containing a bio-soluble
fiber comprising at least one of MgO and CaO, wherein a content of
an alkali metal oxide in the bio-soluble fiber is 2 mass % or less,
and the bio-soluble fiber contains 70 to 95 mass % of
SiO.sub.2.
2. The honeycomb structure according to claim 1, wherein the
bio-soluble fiber has thermal resistance at a temperature of
1200.degree. C. or more.
3. The honeycomb structure according to claim 1, wherein the
bonding material further contains inorganic particles and/or a
colloidal oxide.
4. The honeycomb structure according to claim 3, wherein the
inorganic particles contained in the bonding material are silicon
carbide.
5. The honeycomb structure according to claim 1, wherein the
bonding material further contains an inorganic binder.
6. The honeycomb structure according to claim 1, wherein the
bonding material further contains an organic binder.
7. The honeycomb structure according to claim 1, wherein the
bio-soluble fiber has an average length of 10 to 600 mm, and has an
average diameter of 0.1 to 10 mm.
8. The honeycomb structure according to claim 1, wherein a bonding
material slurry for use as the bonding material has a pH of 0.5 to
10.
9. The honeycomb structure according to claim 1, wherein the
bonding material has a four-point bending strength of 100 to 3000
kPa.
10. The honeycomb structure according to claim 1, wherein the
bonding material has a compression-Young's modulus of 5 to 500
MPa.
11. The honeycomb structure according to claim 1, wherein the
bonding material has a thermal conductivity of 0.1 to 10 W/mK.
12. The honeycomb structure according to claim 1, wherein the
bonding material has a thermal expansion coefficient of
1.times.10.sup.-6 to 8.times.10.sup.-6/K.
13. The honeycomb structure according to claim 1, wherein the
bonding material has a thermal capacity of 400 to 4500
Jm.sup.3/K.
14. The honeycomb structure according to claim 1, wherein the
bonding material has a porosity of 17 to 70%.
15. The honeycomb structure according to claim 1, wherein the
bonding material has a density of 0.5 to 3 g/cm.sup.3.
16. The honeycomb structure according to claim 1, wherein a layer
formed of the bonding material has a thickness of 0.1 to 5 mm.
17. A ceramic bonding material containing a bio-soluble fiber
having thermal resistance at 1200.degree. C. or more and containing
70 to 95 mass % of SiO.sub.2, wherein the bio-soluble fiber
comprises at least one of MgO and CaO, and a content of an alkali
metal oxide in the bio-soluble fiber is 2 mass % or less.
Description
TECHNICAL FIELD
The present invention relates to a honeycomb structure and a
bonding material for use in the structure. More particularly, it
relates to a honeycomb structure which contains a bio-soluble
fiber, whereby environmental safety is improved.
BACKGROUND ART
A honeycomb structure made of a ceramics has been used in a
catalyst carrier for an internal combustion engine, a boiler, a
chemical reaction device, a reformer for a fuel cell and the like
in which a catalyst function is used, a trapping filter of fine
particles in an exhaust gas, particularly diesel fine particles (a
diesel particulate filter, hereinafter sometimes referred to as the
"DPF"), and the like.
In general, as shown in FIGS. 2(a) and 2(b), a honeycomb structure
for use in such purposes has a structure which includes a plurality
of cells 23 constituting fluid channels divided by porous partition
walls 24 and in which adjacent cells 23 are alternatively plugged
on the opposite end portions so that end faces have a checkered
pattern. In a honeycomb structure 21 having such a structure, a
fluid to be treated flows into the cell 23 not plugged on an inflow
hole side end face 25, that is, the cell 23 with a plugged end
portion on an outflow hole side end face 26, and the fluid passes
through the porous partition wall 24, and is discharged from the
adjacent cell 23, that is, the cell 23 with a plugged end portion
on the inflow hole side end face 25 and not plugged on the outflow
hole side end face 26. In this case, the partition walls 24
function as a filter. When the structure is used as, for example,
the DPF, a particulate matter (hereinafter sometimes referred to as
the "PM") such as soot discharged from a diesel engine is trapped
by the partition walls 24 and accumulates on the partition walls
24.
The honeycomb structure used in this manner has a problem such that
a temperature distribution in the honeycomb structure becomes
nonuniform owing to the rapid temperature change of the exhaust gas
or local heat generation, and thereby cracks are generated in the
honeycomb structure. In particular, when the structure is used as
the DPF, a particulate matter such as the accumulated soot needs to
be burnt and removed to regenerate the structure. In this case,
local temperature rise is caused, which results in problems that a
regeneration efficiency lowers owing to the nonuniformity of a
regeneration temperature and that the cracks due to a large thermal
stress are easily generated.
In addition, in a case where the ceramic honeycomb structure
provided with a plurality of cells extending therethrough is used
as a dust-collecting filter for use in a corrosive gas atmosphere
at a high temperature, for example, the diesel particulate filter
(DPF) which traps the particulate matter (PM) discharged from the
diesel engine, owing to the local heat generation accompanying the
abnormal burning of the PM, thermal shock brought by the rapid
temperature change of the exhaust gas, and the like, the nonuniform
temperature distribution is generated in the structure, and the
thermal stress acts. As a result, the ceramic honeycomb structure
might incur the crack generation or melting.
To solve this problem, a method is suggested in which a plurality
of divided segments of the honeycomb structure are bonded with a
bonding material. Specifically, a method for manufacturing the
honeycomb structure in which a large number of honeycomb bodies
(segments) are bonded together with discontinuous bonding materials
is disclosed (for example, see Patent Document 1).
Moreover, a method for manufacturing a thermal-shock-resistant
rotary heat storage type ceramic heat exchanger is suggested in
which the matrix segments of the honeycomb structure constituted of
a ceramic material are formed by extrusion, fired, and then the
outer peripheral portions of the segments are processed to be flat
and smooth. Afterward, the bonding portions of the segments are
coated with a ceramic bonding material in which a fired mineral
composition is substantially the same as that of the matrix
segments and in which a thermal expansion ratio difference is 0.1%
or less at 800.degree. C., and they are fired (for example, see
Patent Document 2).
Furthermore, a ceramic honeycomb structure is disclosed in which
cordierite honeycomb segments are bonded with the same material of
cordierite cement (for example, see Non-Patent Document 1).
In the honeycomb structure in which such honeycomb segments are
integrated using the bonding material, it is an important theme to
secure a bonding strength between the honeycomb segments, but a
bonding defect is sometimes generated. For example, bonding layers
are cracked owing to the difference of the thermal expansion ratio
or a contraction ratio due to the firing between the bonding layers
and the honeycomb segments, or the bonding layers themselves peel.
In particular, in the honeycomb structure of a large size,
especially with a channel (cell) length of 50 mm or more, the
difference of the thermal expansion or the contraction due to the
firing between the bonding layers and the honeycomb segments
remarkably increases. Therefore, there is a problem that it is
difficult to obtain a honeycomb structure of a large size in which
any bonding defect is not generated in the bonding layers (the
bonding portions).
To solve such problems, a honeycomb structure is suggested in which
a plurality of honeycomb segments are securely bonded to one
another without generating any bonding defect such as crack or peel
in the bonding portions of these segments. Moreover, a method for
manufacturing a honeycomb structure having such characteristics is
suggested. Furthermore, a honeycomb structure made of a ceramic
material is suggested in which there a bonding material capable of
bonding together bodies to be bonded without generating any bonding
defect such as the crack or peel in the bonded portions is used. In
the honeycomb structure, a plurality of honeycomb segments provided
with cell structures having a plurality of cells constituting fluid
channels divided by porous partition walls and porous outer walls
on outer peripheries of the cell structures, the bonding material
containing colloidal silica or the like is dried to form the
bonding layers on the outer walls, and the outer walls are bonded
to one another via the bonding layers (see Patent Document 3).
In addition, a ceramic structure is suggested in which a plurality
of ceramic members are united to form an aggregate. Each of the
ceramic members has a plurality of through holes arranged in a
longitudinal direction, and these through holes are plugged on the
end faces so that each of the end faces has a checkered pattern.
Moreover, the through holes have a reversed opening/closing
relation on gas inlet and outlet sides. Furthermore, air can pass
through the adjacent through holes via the porous partition walls.
In the ceramic structure, a portion between the ceramic members is
filled with a material constituted of at least an inorganic fiber,
an inorganic binder, an organic binder, and inorganic particles,
dried, and hardened to form an elastic seal material having a
structure in which the inorganic fiber, the inorganic particles,
and a ceramic material formed by heating and firing the inorganic
binder three-dimensionally cross one another. The respective
ceramic members are integrally bonded via the sealing material. In
particular, as the inorganic particles, at least one or more types
of inorganic powder or whisker selected from the group consisting
of silicon carbide, silicon nitride and boron nitride are used. As
the inorganic fiber, at least one or more ceramic fibers selected
from the group consisting of silica-alumina, mullite, alumina, and
silica are suggested (see Patent Document 4).
With regard to the conventional ceramic fiber, it has been
necessary to consider that there is a possibility of affecting a
human body when particle diameters, a composition, and an existence
form satisfy conditions within certain values. Therefore, to
manufacture the honeycomb structure in consideration of health, a
new approach different from the above conventional technology has
been demanded.
Thus, as a honeycomb structure using a bio-soluble fiber, a
honeycomb structure formed of nonwoven cloth using the bio-soluble
fiber is suggested. This honeycomb structure is formed by
alternately laminating flat-plate-like nonwoven cloth and
waveform-like nonwoven cloth, and the nonwoven cloth is formed of
the bio-soluble fiber and a binder (see Patent Document 5).
Therefore, the presence of the binder is essential for this
honeycomb structure of Patent Document 5, and the structure could
not be used in the heretofore used honeycomb structure and the
bonding material for the structure. Moreover, the structure is
thermally resistant to 800.degree. C. or more, and hence the
structure cannot sufficiently bear the use at 1200.degree. C. or
more as a honeycomb structure made of a ceramics for use as a
catalyst carrier for an internal combustion engine, a boiler, a
chemical reaction device, a reformer for a fuel cell, or the like
in which a catalyst function is used, or as a DPF or the like which
traps a PM in an exhaust gas. Patent Document 1: U.S. Pat. No.
4,335,783 Patent Document 2: JP-B-61-51240 Patent Document 3:
JP-A-2005-154202 Patent Document 4: JP Patent No. 3121497 Patent
Document 5: JP-A-2003-105662 Non-Patent Document 1: SAE Paper
860008 (1986)
DISCLOSURE OF THE INVENTION
The present invention has been developed in view of the problem of
such a conventional technology, and an object thereof is to provide
a honeycomb structure having a performance equivalent to that of a
heretofore generally used honeycomb structure containing a ceramic
fiber in a bonding material while any influence on the health of a
human body does not have to be considered. A further object thereof
is to suggest a bonding material using a fiber which obviates the
need for considering any influence on the health of a human body as
the bonding material of the honeycomb structure.
To achieve the above objects, the present inventors have earnestly
continued researches and eventually developed the following
invention. That is, according to the present invention, the
following honeycomb structure and a bonding material for use in
manufacturing the honeycomb structure are provided.
[1] A honeycomb structure made of a ceramics, consisting of a
plurality of honeycomb segments provided with cell structures
having a plurality of cells constituting fluid channels divided by
porous partition walls and porous outer walls on outer peripheries
of the cell structures, and integrated by bonding the outer walls
to one another with a bonding material, wherein the bonding
material contains a bio-soluble fiber.
[2] The honeycomb structure according to the above [1], wherein the
bio-soluble fiber has thermal resistance at a temperature of
1200.degree. C. or more.
[3] The honeycomb structure according to the above or [2], wherein
the bio-soluble fiber contains 60 to 95 mass % of SiO.sub.2.
[4] The honeycomb structure according to any one of the above [1]
to [3], wherein the content of an alkali metal oxide in the
bio-soluble fiber is 2 mass % or less.
[5] The honeycomb structure according to any one of the above [1]
to [4], wherein the bonding material further contains inorganic
particles and/or a colloidal oxide.
[6] The honeycomb structure according to the above [5], wherein the
inorganic particles contained in the bonding material are silicon
carbide.
[7] The honeycomb structure according to any one of the above [1]
to [6], wherein the bonding material further contains an inorganic
binder.
[8] The honeycomb structure according to any one of the above [1]
to [7], wherein the bonding material further contains an organic
binder.
[9] The honeycomb structure according to any one of the above [1]
to [8], wherein the bio-soluble fiber has an average length of 10
to 600 .mu.m, and has an average diameter of 0.1 to 10 .mu.m.
[10] The honeycomb structure according to any one of the above [1]
to [9], wherein a bonding material slurry for use as the bonding
material has a pH of 0.5 to 10.
[11] The honeycomb structure according to any one of the above [1]
to [10], wherein the bonding material has a four-point bending
strength of 100 to 3000 kPa.
[12] The honeycomb structure according to any one of the above [1]
to [11]), wherein the bonding material has a compression Young's
modulus of 5 to 500 MPa.
[13] The honeycomb structure according to any one of the above [1]
to [12], wherein the bonding material has a thermal conductivity of
0.1 to 10 W/mK.
[14] The honeycomb structure according to any one of the above [1]
to [13], wherein the bonding material has a thermal expansion
coefficient of 1.times.10.sup.-6 to 8.times.10.sup.-6/K.
[15] The honeycomb structure according to any one of the above [1]
to [14], wherein the bonding material has a thermal capacity of 400
to 4500 Jm.sup.3/K.
[16] The honeycomb structure according to any one of the above [1]
to [15], wherein the bonding material has a porosity of 17 to
70%.
[17] The honeycomb structure according to any one of the above [1]
to [16], wherein the bonding material has a density of 0.5 to 3
g/cm.sup.3.
[18] The honeycomb structure according to any one of the above [1]
to [17], wherein a layer formed of the bonding material has a
thickness of 0.1 to 5 mm.
[19] A ceramic bonding material containing a bio-soluble fiber
having thermal resistance at 1200.degree. C. or more and containing
60 to 95 mass % of SiO.sub.2.
In the honeycomb structure of the present invention, a bonding
material constituted of a component in which any influence on the
health of a human body does not have to be considered is dried to
form a bonding layer, and outer walls are bonded to one another via
these bonding layers, hence environment safety is improved.
Moreover, the honeycomb structure of the present invention produces
an effect that honeycomb segments are securely bonded to one
another without generating any bonding defect such as crack or peel
in bonding portions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(a) is a diagram showing one embodiment of a honeycomb
structure according to the present invention, and is a perspective
view showing a honeycomb segment;
FIG. 1(b) is a diagram showing one embodiment of a honeycomb
structure according to the present invention, and is a perspective
view showing the honeycomb structure;
FIG. 1(c) is a diagram showing one embodiment of a honeycomb
structure according to the present invention, and is a top plan
view showing the honeycomb structure;
FIG. 2(a) is a diagram showing a general honeycomb structure, and
is a perspective view showing the honeycomb structure; and
FIG. 2(b) is a diagram showing a general honeycomb structure, and
is a partially enlarged plan view showing an end face of the
honeycomb structure.
DESCRIPTION OF REFERENCE NUMERALS
1: honeycomb structure, 2: partition wall, 3: cell, 5: cell
structure, 7: outer wall, 8: bonding layer, 12: honeycomb segment,
21: honeycomb structure, 23: cell, 24: partition wall, 25: inflow
hole side end face, 26: outflow hole side end face.
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will hereinafter be
described, but it should be understood that the present invention
is not limited to the following embodiment, and is appropriately
subjected to design change, improvement, and the like based on the
ordinary knowledge of any one skilled in the art within the scope
of the present invention.
FIGS. 1(a) to 1(c) are diagrams showing one embodiment of a
honeycomb structure according to the present invention, FIG. 1(a)
is a perspective view showing a honeycomb segment, FIG. 1(b) is a
perspective view showing the honeycomb structure, and FIG. 1(c) is
a top plan view showing the honeycomb structure. In a honeycomb
structure 1 of the present embodiment consisting of a plurality of
honeycomb segments 12 provided with cell structures 5 having a
plurality of cells 3 constituting fluid channels divided by porous
partition walls 2 and porous outer walls 7 on outer peripheries of
the cell structures 5, and integrated by bonding the outer walls 7
to one another with a bonding material, the bonding material
contains a bio-soluble fiber. In the honeycomb structure 1 of the
present embodiment, this bonding material is dried to form bonding
layers 8 on the outer walls 7, and the outer walls 7 are bonded to
one another via the bonding layers 8.
The "bio-soluble fiber" is a fiber which is non-durable in a
physiological solution and which is other than the control target
of cancer-causing classification. The examples of the physiological
solution include physiological saline (a 0.9% sodium chloride
solution), a buffer solution, a pseudo body fluid and serum. The
pseudo body fluid is an aqueous solution which contains
substantially the same component as a human plasma component.
The "fiber" is a material having a length which is larger than a
width. In a specific embodiment, a fiber having a length at least
five times, ten times or 100 times the diameter thereof can
appropriately be selected and used in accordance with a
purpose.
In general, the bio-soluble fiber is dissolved or substantially
dissolved in the physiological solution within about one year. To
be "substantially dissolved" means to be dissolved as much as at
least about 75 mass %.
In general, examples of the bio-soluble fiber for use in the
present embodiment include inorganic oxides such as Na.sub.2O,
K.sub.2O, CaO, MgO, P.sub.2O.sub.5, Li.sub.2O, BaO, and a
combination of them with silica. Other metal oxides or other
ceramic components may be contained in the bio-soluble fiber.
However, these components themselves do not have any desired
solubility, and are present in such a sufficiently small amount
that the fiber can entirely be decomposed in the physiological
solution. Examples of such a metal oxide include Al.sub.2O.sub.3,
TiO.sub.2, ZrO.sub.2, B.sub.2O.sub.3, and iron oxides. The
bio-soluble fiber may contain a metal component in such an amount
that the fiber can be decomposed in the physiological solution.
The content of SiO.sub.2 in the bio-soluble fiber for use in the
present embodiment is preferably 60 mass % or more, especially
preferably 65 mass % to 95 mass %. With regard to the bio-soluble
fiber having such a composition, the fiber is immobilized at a time
when the inorganic binder is used in the bonding material, so that
a sufficient strength is preferably exerted, and further thermal
resistance is especially preferably imparted.
Furthermore, in the bio-soluble fiber for use in the present
embodiment, the content of the alkali metal oxide is preferably 2
mass % or less. Here, examples of the alkali metal oxide include
Na.sub.2O and K.sub.2O. When the content of the alkali metal oxide
is 2 mass % or less, the lowering of the strength of the bonding
material during use at a high temperature of, for example,
1200.degree. C. or more can be prevented.
Examples of the bio-soluble fiber for use in the present embodiment
include fibers containing silica, magnesium, silica, the oxide of
magnesium and the oxide of calcium. Such a fiber is usually
referred to as a magnesium silicate or calcium magnesium silicate
fiber.
The bio-soluble fiber is sold with a trade name of, for example,
Super Wool from Shinnikka Thermal Ceramics Corporation. For
example, Super Wool 607 contains 60 to 70 mass % of SiO.sub.2, 25
to 35 mass % of CaO, 4 to 7 mass % of MgO and a small amount of
Al.sub.2O.sub.3. Super Wool 607 Max contains 60 to 70 mass % of
SiO.sub.2, 16 to 22 mass % of CaO, 12 to 19 mass % of MgO and a
small amount of Al.sub.2O.sub.3.
The bio-soluble fiber for use in the present embodiment may have
various average diameter and length. For example, a commercially
available fiber has an average fiber diameter in a range of about
0.05 to 15 .mu.m. In particular, as the bio-soluble fiber, a fiber
having an average fiber diameter in a range of 0.1 to 10 .mu.m may
preferably be used. An average length in a major axis direction is
preferably 10 to 600 .mu.m, further preferably 50 to 400 .mu.m.
When the average length in the major axis direction is below 10
.mu.m, elasticity sometimes cannot be imparted to the bonding layer
constituted of the bonding material. When the length exceeds 600
pmt, a coating property sometimes lowers.
The bonding material for use in the present embodiment contains the
bio-soluble fiber. In addition, the material preferably contains,
for example, an inorganic binder, an organic binder, inorganic
particles, foam particles and the like.
Examples of the above inorganic binder include silica sol and
alumina sol. They may be used alone or as a combination of two or
more of them.
Examples of the above organic binder include polyvinyl alcohol
(PVA), carboxymethyl cellulose (CMC) and methyl cellulose (NC). The
adhesion of an interface between the bonding material and the
segment is effectively improved. Examples of the inorganic
particles include ceramics such as silicon carbide, silicon
nitride, cordierite, alumina, and mullite.
Moreover, the slurry of the bonding material for use in
manufacturing the honeycomb structure of the present embodiment has
a pH in a range of preferably 0.5 to 10, further preferably 2 to 8.
When the pH is below 0.5, or 10 or more, the stability of the
slurry lowers, and the coating property sometimes lowers. Moreover,
the bonding between inorganic binders such as silica sol and
alumina sol is disturbed, and the bonding material is sometimes
easily cracked.
In the honeycomb structure of the present embodiment, the
four-point bending strength of the bonding material (the bonding
layer) is preferably in a range of 100 to 3000 kPa. In a case where
the four-point bending strength of the bonding material is below
100 kPa, in the honeycomb structure in which the plurality of
honeycomb segments are integrated with the bonding material, the
strength of the bonding portions cannot be secured, and the bonding
portions sometimes break owing to the rapid thermal stress
generated during the regeneration of the DPF. On the other hand,
when the strength is beyond 3000 MPa, the stress cannot be relaxed,
and the honeycomb segments are sometimes cracked and broken owing
to the rapid thermal stress generated during the regeneration of
the DPF. The four-point bending strength functions further
preferably in a range of 500 to 2000 kPa. It is to be noted that
the four-point bending strength mentioned in the present
description is a value measured in conformity to JIS R 1601
"Bending Strength Test Method of Fine Ceramics".
The compression Young's modulus in the Z-axis direction of the
bonding material (the bonding layer) for use in the present
embodiment is in a range of 5 to 500 MPa. In a case where the
compression Young's modulus of the bonding material in the Z-axis
direction is below 5 MPa, when there is a temperature distribution
inside the honeycomb segments, the honeycomb segments themselves
are largely deformed, and are sometimes cracked. On the other hand,
in a case where the modulus is beyond 500 MPa, in the honeycomb
structure in which a plurality of honeycomb segments are integrated
with the bonding material regardless of the length of the honeycomb
segments, the stress cannot be relaxed, and the outer peripheral
portion of the structure is sometimes broken owing to the rapid
thermal stress generated during the regeneration of the DPF. The
compression Young's modulus is further preferably in a range of 5
to 100 MPa. It is to be noted that the compression Young's modulus
of the bonding material in the Z-axis direction mentioned in the
present description is a value calculated from a load and a
displacement curve.
The porosity of the bonding material (the bonding layer) for use in
the present embodiment is preferably 17 to 70%, further preferably
22 to 54%. When the porosity is below 17%, the Young's modulus
increases, and a stress relaxation function sometimes cannot
sufficiently be exerted. When the porosity exceeds 70%, the bonding
strength between the honeycomb segment and the bonding material
sometimes lowers. It is to be noted that the porosity can be
measured with a mercury porosimeter or by Archimedes process. The
above porosity values are values measured by the Archimedes
process.
The bulk density of the bonding material (the bonding layer) for
use in the present embodiment is preferably 0.5 to 3 g/cm.sup.3,
further preferably 0.8 to 2 g/cm.sup.3. When the bulk density
exceeds 3 g/cm.sup.3, the Young's modulus increases, and the stress
relaxation function sometimes cannot sufficiently be exerted. When
the bulk density is below 0.5 g/cm.sup.3, the bonding strength
between the honeycomb segment and the bonding material sometimes
lowers. It is to be noted that the bulk density mentioned in the
present description is a value measured by the Archimedes
process.
The thermal conductivity of the bonding material (the bonding
layer) for use in the present embodiment is preferably 0.1 to 10
W/mK, further preferably 0.3 to 5 W/mK. When the thermal
conductivity is below 0.1 W/mK, a maximum temperature during the
regeneration increases. When the thermal conductivity exceeds 10
W/mK, a temperature gradient inside the segment increases, and the
segment is sometimes easily cracked during the regeneration. It is
to be noted that the thermal conductivity mentioned in the present
description is a value measured by a laser flash process, using a
cut bonding layer portion.
The thermal expansion coefficient of the bonding material (the
bonding layer) for use in the present embodiment is preferably
1.times.10.sup.-6 to 8.times.10.sup.-6/K, further preferably
3.times.10.sup.-6 to 6.times.10.sup.-6/K. When the thermal
expansion coefficient of the bonding material is below
1.times.10.sup.-6/K, the interface between the bonding material and
the honeycomb segment is sometimes easily cracked owing to the
mismatching of the thermal expansion coefficient between the
segment material and the bonding material during the regeneration.
When the thermal expansion coefficient of the bonding material
exceeds 8.times.10.sup.-6/K, the bonding material is sometimes
easily cracked during the regeneration. It is to be noted that the
above-mentioned thermal expansion coefficient is a value in a
temperature range of room temperature to 800.degree. C.
The thermal capacity of the bonding material (the bonding layer)
for use in the present embodiment is preferably 250 to 4500
Jm.sup.3/K, further preferably 500 to 3000 Jm.sup.31K. When the
thermal capacity of the bonding material is below 250 Jm.sup.3/K, a
maximum temperature during the regeneration increases, and the
segment is sometimes easily cracked. When the thermal capacity of
the bonding material exceeds 4500 Jm.sup.3/K, the temperature
during the regeneration does not rise, and a temperature rise
characteristic sometimes lowers. It is to be noted that the thermal
capacity mentioned in the present description is a value calculated
by multiplying, by the density, specific heat obtained by a laser
flash process or with a differential thermal flow rate meter.
In the present embodiment, there is not any special restriction on
the thickness of the bonding material (the bonding layer). However,
when the material is excessively thick, a pressure loss excessively
increases when exhaust gas passes therethrough. When the material
is excessively thin, the bonding material unfavorably does not
exert a sufficient bonding capability. The thickness of the bonding
material (the bonding layer) is preferably 0.1 to 5.0 mm, further
preferably 0.5 to 3.0 mm.
In the present invention, there is not any special restriction on
the cell density (the number of the cells per unit cross-sectional
area perpendicular to the channel) of the honeycomb segment.
However, when the cell density is excessively small, a geometric
surface area runs short. When the cell density is excessively
large, the pressure loss unfavorably excessively increases. The
cell density is preferably 0.9 to 310 cells/cm.sup.2 (6 to 2000
cells/square inch). Moreover, there is not any special restriction
on the cross-sectional shape of a cell (a cross section
perpendicular to the channel), and there may be used a polygonal
shape such as a triangular shape, a quadrangular shape, or a
hexagonal shape, a circular shape, an elliptic shape, a combination
of a octagonal shape and a quadrangular shape, or any shape such as
a corrugated shape. From a viewpoint of manufacturing, a triangular
shape, a quadrangular shape, a combination of the octagonal shape
and a quadrangular shape, or a hexagonal shape is preferable.
Moreover, there is not any special restriction on the thickness of
the partition wall. However, when the partition wall is excessively
thin, the strength of the honeycomb segment becomes insufficient.
When the partition wall is excessively thick, the pressure loss
unfavorably excessively increases. The thickness of the partition
wall is preferably in a range of 50 to 2000 .mu.m.
Moreover, there is not any special restriction on the shape of the
honeycomb segment, and any shape may be used. For example, a
plurality of square pole shown in FIG. 1(a) as a basic shape are
preferably bonded and integrated as shown in FIG. 1(b). It is also
preferable that the shape of the honeycomb segment 12 constituting
the outermost peripheral surface of the honeycomb structure 1 is
matched with the outer peripheral shape of the honeycomb structure
1. Furthermore, the shape of the cross section of each honeycomb
segment perpendicular to the channel at may be a fan shape.
Furthermore, in the honeycomb structure, there is not any special
restriction on the shape of the cross section perpendicular to the
channel, and there may be used a circular shape such as a perfect
circular shape, an elliptic shape, or an oval shape, a polygonal
shape such as a triangular shape, a quadrangular shape, or a
pentagonal shape, or any shape such as an amorphous shape. In
addition, when the honeycomb structure of the present embodiment is
used as the catalyst carrier to be incorporated in an internal
combustion engine, a boiler, a chemical reaction device, a reformer
for a fuel cell, or the like, the honeycomb structure preferably
carries a metal having a catalyst capability. Typical examples of
the metal having the catalyst capability include platinum (Pt),
palladium (Pd), and rhodium (Rd). At least one of these metals is
preferably carried by the honeycomb structure.
On the other hand, when the honeycomb structure of the present
invention is used as a filter such as a DPF for trapping and
removing a particulate matter (soot) contained in the exhaust gas,
preferably, openings of the predetermined cells are plugged in one
end face, and openings of the remaining cells are plugged in the
other end face. It is also preferable that adjacent cells are
plugged alternatively on the opposite end portions so that the end
faces have a checkered pattern. The cells are plugged in this
manner, whereby the soot-containing exhaust gas which has flowed
into one end face side of the honeycomb structure passes through
the partition walls, and is discharged from the other end face
side. However, when the exhaust gas passes through the partition
walls, the porous partition walls can perform the function of the
filter to trap the soot. It is to be noted that when the trapped
soot is accumulated on the partition walls, the pressure loss
increases, so that a burden is imposed on the engine, and a fuel
efficiency and drivability lower. Therefore, the soot is regularly
burnt and removed by heating means such as a heater to regenerate
the filter function. To promote the burning during this
regeneration, the honeycomb structure may carry the above-described
metal having the catalyst capability.
It is to be noted that as the material of the honeycomb segment for
use in the present invention, there may be used one material
selected from the group consisting of cordierite, mullite, alumina,
spinel, silicon carbide, metal silicon, a silicon-silicon carbide
based composite material, a silicon carbide-cordierite based
composite material, silicon nitride, lithium aluminum silicate, and
an Fe--Cr--Al based metal, or a combination of a plurality of
materials selected from the group.
The honeycomb structure of the present invention is manufactured by
bonding the honeycomb segments with the bonding material. As the
raw materials of the honeycomb segments, for example, a binder such
as methyl cellulose or hydroxymethyl cellulose, a surfactant,
water, and the like are added to the above-mentioned material, and
kneaded to form a plastic clay. Subsequently, the resultant clay is
extruded and formed in a forming step, to form a formed honeycomb
body having a plurality of cells constituting fluid channels
divided by partition walls. During the extrusion forming, a plunger
type extruder, a biaxial screw type continuous extruder or the like
may be used. When the biaxial screw type continuous extruder is
used, a clay step and a forming step can continuously be performed.
The resultant formed honeycomb body can be dried by, for example,
microwaves, dielectric heating and/or hot air, and then fired to
obtain a fired honeycomb body.
The resultant fired honeycomb body is processed into a honeycomb
segment having a predetermined shape by use of means such as a band
saw or a metal saw, if necessary. In this manner, the
square-pole-like honeycomb segment having a bonding surface (an
outer wall) can be obtained. These honeycomb segments can be bonded
to one another with a bonding material containing the
above-mentioned bio-soluble fiber to obtain a honeycomb structure.
There is not any special restriction on a method for coating the
honeycomb segment with the bonding material, and, for example, a
spray process, a coating process using a brush, a stylus or the
like, a dipping process, or the like may be employed.
It is to be noted that at least a part of the outer surface of the
honeycomb structure (a bonded body) formed by bonding the honeycomb
segments to one another may be removed, if necessary. Specifically,
for example, preferably two or more cells, further preferably two
to four cells are removed from the outermost periphery. Here, to
remove the cells is to remove at least a part of the partition
walls forming the cells to obtain a state in which four peripheries
are completely not surrounded with the partition walls.
When at least a part of the outer periphery of the bonded body is
removed, the corresponding portion is coated with a coating
material to form the outer peripheral wall of the honeycomb
structure. The coating material preferably contains at least one
selected from the group consisting of colloidal silica, colloidal
alumina, a ceramic fiber, ceramic particles, an organic binder, an
inorganic binder, and hollow particles. Examples of the ceramic
particles include silicon carbide, cordierite, silica, alumina, and
zirconia.
Next, one embodiment of a ceramic bonding material according to the
present invention will be described. The ceramic bonding material
of the present embodiment is a ceramic bonding material which
contains the bio-soluble fiber having thermal resistance at
1200.degree. C. or more and containing 60 to 95 mass % of
SiO.sub.2. This ceramic bonding material may preferably be used as
a bonding material in bonding the honeycomb segments to one another
in the honeycomb structure of the present invention. The ceramic
bonding material of the present embodiment can securely bond the
honeycomb segments to one another without generating a bonding
defect such as crack or peel in bonded portions. The components in
which any influence on the health of a human body does not have to
be considered are used, so that an environment safety is
improved.
As the bio-soluble fiber contained in the ceramic bonding material
of the present embodiment, a fiber constituted in the same manner
as in the bio-soluble fiber for use in the above bonding material
of the honeycomb structure according to the present invention may
preferably be used.
EXAMPLES
The present invention will hereinafter specifically be described in
accordance with examples, but the present invention is not limited
to these examples.
1. Manufacturing of Honeycomb Segment:
As a honeycomb segment raw material, SiC powder and metal Si powder
were mixed at a mass ratio of 80:20, and starch and a foam resin as
pore formers, further methyl cellulose, hydroxypropoxyl methyl
cellulose, a surfactant, and water were added to the material to
prepare a plastic clay. This clay was extruded, formed, and dried
by microwaves and hot air to obtain a honeycomb segment formed body
including partition walls having a thickness of 310 .mu.m, having a
cell density of about 46.5 cells/cm.sup.2 (300 cells/square inch),
having a square section with each 35 mm long side and having a
length of 152 mm. In this honeycomb segment formed body, both end
faces of the cells were plugged so that the end faces had a
checkered pattern. That is, the cells were plugged so that adjacent
cells were plugged alternatively on the opposite end portions. As a
plugging material, a material similar to the honeycomb segment raw
material was used. The both end faces of the cells were plugged,
dried, then degreased in the atmosphere at about 400.degree. C.,
and then fired in an Ar inactive atmosphere at about 1450.degree.
C. to obtain the honeycomb segment having a porous structure in
which SiC crystal particles were bonded with Si.
2. Preparation of Bonding Material (Bonding Materials A to H):
40 mass % of SiC powder as inorganic particles having an average
diameter of 2 .mu.m, 30 mass % of an aqueous solution containing 40
mass % of silica gel as an inorganic binder, 1 mass % of clay and
29 mass % of bio-soluble fiber having characteristics shown in
Table 2 were mixed. Water was added to the resultant mixture, and
the mixture was kneaded using a mixer for 30 minutes to obtain
bonding materials A to F having composition and characteristics
shown in Table 1. Moreover, instead of the bio-soluble fiber, an
alumino silicate fiber for use in manufacturing a conventional
honeycomb structure was mixed at an equal amount ratio to obtain a
bonding material G, and an alumina fiber was similarly mixed to
obtain a bonding material H. These fibers had an average diameter
of 5 .mu.m and an average length of 50 .mu.m.
TABLE-US-00001 TABLE 1 Characteristics of bio-soluble fiber Alkali
metal Thermal SiO.sub.2 MgO CaO oxide Bonding resistance amount
amount amount amount material (.degree. C.) (mass %) (mass %) (mass
%) (mass %) A 1260 70 29.5 -- 0.5 B 1260 65 34 -- 1.0 C 1000 60 --
-- 1.2 D 1000 50 -- -- 1.5 E 1260 60 37 -- 3.0 F 700 40 -- --
10.0
3. Manufacturing of Honeycomb Structure
Examples 1 to 6 and Comparative Examples 1, 2
Subsequently, 16 honeycomb segments were bonded to one another by
use of the bonding materials (the bonding materials A to H) shown
in Table 1, and dried at 200.degree. C. for 2 hours. Afterward, an
outer peripheral portion was ground so as to obtain a cylindrical
shape, and the corresponding portion was coated with a coating
material and subjected to a thermal treatment at 500.degree. C. for
2 hours, to obtain honeycomb structures (Examples 1 to 6 and
Comparative Examples 1, 2).
4. Evaluation and Results
Examples 1 to 6 and Comparative Examples 1, 2
These honeycomb structures (Examples 1 to 6 and Comparative
Examples 1, 2) were attached to the exhaust tube of a diesel
engine, and 8 g/L of soot was accumulated. Afterward, the soot was
regenerated so that the center of each honeycomb structure had a
temperature of 1200.degree. C. With regard to the tested honeycomb
structures, the appearances of honeycomb segments and bonding
layers were observed with an optical microscope. Moreover, a part
of the bonding layers was cut out, and fiber shapes were confirmed
with an SEM. Ten samples for a predetermined strength test were cut
from each structure, and subjected to measurement of a three-point
bending bonding strength according to JIS R 1601. The evaluation
results are shown in Table 2.
TABLE-US-00002 TABLE 2 Bonding Honey- Bonding material Fiber comb
Bonding strength used shape segment layer [MPa] Example 1 A No
change No crack No crack 3.8 Example 2 B No change No crack No
crack 3.5 Example 3 C Partial Cracked No crack 2.9 melting Example
4 D Partial Cracked Cracked 1.5 melting Example 5 E No change
Cracked Cracked 1.2 Example 6 F Partial Cracked Cracked 0.6 melting
Comparative G No change No crack No crack 3.5 Example 1 Comparative
H No change No crack No crack 3.2 Example 2
5. Preparation of Bonding Material (Bonding Material A-1 to
A-18)
The same composition as that of the bonding material A used in
Example 1 was used, and an organic binder, a foam resin, a
dispersant, and the like were added to a bio-soluble fiber having a
shape shown in Tables 3 and 4, and blended therewith as shown in
Tables 3 and 4, to prepare bonding materials A-1 to A-18. Tables 3
and 4 show the blend prescriptions of the bonding materials A-1 to
A-18. The porosity (%) and bulk density (g/cm.sup.3) of the bonding
layer were measured using samples cut from bonding layers formed of
the bonding materials A-1 to A-18. It is to be noted that the
porosity and bulk density of the bonding layer were measured by
Archimedes process.
TABLE-US-00003 TABLE 3 Inorganic fiber Average Average diameter of
Organic Bulk Bonding length cross section binder Dispersant pH of
bonding density material [.mu.m] [.mu.m] [mass %] [mass %] material
slurry Porosity [%] [g/cm.sup.3] Others A-1 50 5 -- 0.3 6.0 45 1.6
Dispersant: 0.3 mass % Foam resin: 1.0 mass % A-2 300 5 -- 0.5 6.0
50 1.4 Dispersant: 0.5 mass % Foam resin: 1.0 mass % A-3 500 5 --
0.7 6.0 65 1.0 Dispersant: 0.7 mass % Foam resin: 1.0 mass % A-4
300 5 CMC 0.3 5.0 60 1.1 Dispersant: 0.3 mass % 0.1 Foam resin: 1.0
mass % A-5 300 5 CMC 0.3 5.0 60 1.1 Dispersant: 0.3 mass % 0.4 Foam
resin: 1.0 mass % A-6 300 5 CMC 0.3 5.0 60 1.1 Dispersant: 0.3 mass
% 0.8 Foam resin: 1.0 mass % A-7 200 5 PVA -- 1.0 60 1.1 Foam
resin: 1.0 mass % 1.0 pH adjustment in HCl A-8 300 5 PVA -- 8.0 60
1.1 Foam resin: 1.0 mass % 1.0 pH adjustment in NaOH A-9 200 5 --
-- 4.8 50 1.6 SiC powder particle diameter: 50 .mu.m *1 CMC is
carboxymethyl cellulose. *2 PVA is polyvinyl alcohol.
TABLE-US-00004 TABLE 4 Inorganic fiber Average pH of Average
diameter of Organic bonding Bonding length cross section binder
material Bulk density material [.mu.m] [.mu.m] [mass %] slurry
Porosity [%] [g/cm.sup.3] Others A-10 200 5 -- 4.8 47 1.8 SiC
powder particle diameter: 100 .mu.m A-11 200 5 -- 4.7 42 2.0 SiC
powder particle diameter: 100 .mu.m SiC powder amount: 60 mass %
A-12 5 0.05 -- 6.0 45 1.6 Foam resin: 1.0 mass % A-13 800 15 -- 6.0
72 0.8 Foam resin: 1.0 mass % A-14 50 5 -- 0.3 45 1.6 Foam resin:
1.0 mass % pH adjustment with HCl A-15 50 5 -- 11 45 1.6 Foam
resin: 1.0 mass % pH adjustment with NaOH A-16 50 5 -- 6.0 80 0.4
Foam resin: 8.0 mass % A-17 50 5 -- 6.0 35 3.1 Silica gel was
changed to alumina gel SiC powder was changed to alumina powder
A-18 50 5 -- 4.5 35 2.5 SiC powder particle diameter: 100 .mu.m
6. Manufacturing of Honeycomb Structures
Examples 7 to 27
Subsequently, 16 honeycomb segments were bonded to one another by
use of bonding materials (bonding materials A-1 to A-18) shown in
Tables 5 and 6, and dried at 200.degree. C. for 2 hours. Afterward,
an outer peripheral portion was ground so as to obtain a
cylindrical shape, and the corresponding portion was coated with a
coating material, and subjected to a thermal treatment at
500.degree. C. for 2 hours, to obtain honeycomb structures
(Examples 7 to 27).
TABLE-US-00005 TABLE 5 4-point Compression Thermal Bonding bending
Young's Thermal expansion Thermal material Bonding strength modulus
conductivity coefficient capacity thickness B-SP- E-SP E/G material
[kPa] [MPa] [W/mK] [.times.10.sup.-6] [m.sup.-3/K] [mm] test tes- t
test Example 7 A-1 600 200 1.0 4.5 1000 1 800.degree. C.
.circleincircle. .circleincircle. Example 8 A-2 550 150 0.7 4.5 800
1 900.degree. C. .circleincircle. .circleincircle. Example 9 A-3
400 130 0.5 4.5 700 1 850.degree. C. .circleincircle.
.circleincircle. Example 10 A-4 900 80 0.6 4.5 800 1 1000.degree.
C. .circleincircle. .circleincircle. Example 11 A-5 1000 50 0.5 4.5
800 1 1100.degree. C. .circleincircle. .circleincircle. Example 12
A-6 1000 50 0.5 4.5 800 1 1100.degree. C. .circleincircle.
.circleincircle. Example 13 A-7 500 80 0.5 4.5 800 1 800.degree. C.
.circleincircle. .circleincircle. Example 14 A-8 500 80 0.5 4.5 800
1 800.degree. C. .circleincircle. .circleincircle. Example 15 A-9
1000 80 1.5 4.5 1100 1 1000.degree. C. .circleincircle.
.circleincircle. Example 16 A-10 1300 90 2.0 4.5 1300 1
1100.degree. C. .circleincircle. .circleincircle. Example 17 A-11
1500 100 3.0 4.4 1300 1 1100.degree. C. .circleincircle.
.circleincircle. Example 18 A-11 1500 100 3.0 4.4 1300 3
1200.degree. C. .circleincircle. .circleincircle.
TABLE-US-00006 TABLE 6 4-point Compression Thermal Bonding bending
Young's Thermal expansion Thermal material Bonding strength modulus
conductivity coefficient capacity thickness B-SP- E-SP E/G material
[kPa] [MPa] [W/mK] [.times.10.sup.-6] [m.sup.-3/K] [mm] test tes- t
test Example 19 A-1 600 200 1.0 4.5 1000 0.05 500.degree. C.
.circleincircle. .largecircle. Example 20 A-1 600 200 1.0 4.5 1000
6 900.degree. C. .largecircle. .largecircle. Example 21 A-12 300
250 0.9 4.5 1000 1 500.degree. C. .largecircle. .largecircle.
Example 22 A-13 300 110 0.8 4.5 680 1 500.degree. C.
.circleincircle. .largecircle. Example 23 A-14 250 200 1.0 4.5 800
1 400.degree. C. .circleincircle. .largecircle. Example 24 A-15 250
200 1.0 4.5 800 1 400.degree. C. .circleincircle. .largecircle.
Example 25 A-16 90 20 0.05 4.5 350 1 300.degree. C. .largecircle.
.largecircle. Example 26 A-17 1000 300 1.4 8.5 1500 1 500.degree.
C. .largecircle. .largecircle. Example 27 A-18 2000 300 11.0 4.3
1600 1 800.degree. C. .circleincircle. .largecircle.
Samples having a predetermined dimension were cut from the bonding
layers of the honeycomb structures of Examples 7 to 27, and a
four-point bending strength, a compression Young's modulus in a
Z-axis direction (hereinafter sometimes simply referred to as the
"compression Young's modulus"), a thermal conductivity, a thermal
expansion coefficient and a thermal capacity were measured. To
measure the four-point bending strength and the thermal expansion
coefficient, rod-like samples having a size of 4 mm.times.30 mm and
a thickness of 0.5 to 3 mm were used, and to measure the rest,
samples having a size of 10.times.10 mm to 30.times.30 mm and a
thickness of 0.5 to 3 mm were used. Methods for the each
measurement will hereinafter be described. Moreover, the honeycomb
structures of Examples 7 to 27 were subjected to a burner-spalling
test (B-sp test), an electric furnace spalling test (E-sp test) and
an engine test (E/G test). Evaluation results are shown in Tables 5
and 6. Methods for the each test will hereinafter be described.
[four-point bending strength]: The four-point bending strength was
measured using the samples cut from the bonding layers in
accordance with JIS R 1601 [bending strength Test Method of Fine
Ceramics].
[Compression Young's modulus in Z-axis direction (compression
Young's modulus)]: The modulus was calculated from a weight and a
displacement curve in the samples cut from the bonding layers.
[Thermal conductivity]: A bonding layer portion was cut out to
measure the thermal conductivity by a laser flash process.
[Thermal capacity]: The thermal capacity was calculated by
multiplying, by a density, specific heat obtained by the laser
flash process or with a differential thermal flow rate meter.
[B-sp test; burner spalling test (rapid heating test)]: Air heated
with a burner was supplied through the honeycomb structure to make
a temperature difference between the center and an outer portion,
and thermal shock resistance was evaluated in accordance with a
temperature at which no crack was generated in the honeycomb
structure. The temperature (.degree. C.) in the test result is the
maximum temperature at which no crack was generated. When this
temperature is high, the thermal shock resistance is high.
[E-sp test; electric furnace spalling test (rapid cooling test)]:
The honeycomb structure was heated in an electric furnace at
500.degree. C. for 2 hours to obtain a uniform temperature.
Afterward, the heated honeycomb structure was taken out of the
electric furnace at room temperature, and the thermal shock
resistance was evaluated in accordance with the presence of cracks
generated in the honeycomb structure. A case where no crack
generation was recognized is shown by a "double circle" mark, and a
case where the generation of a very small amount of cracks was
recognized is shown by a "circle" mark. A case where the generation
of a large amount of cracks was recognized is shown by a "cross"
mark.
[Engine test (E/G test)]: On conditions that particulates
accumulated were burnt to regenerate the filter so that the center
of the honeycomb structure had a temperature of 1000.degree. C.,
the thermal shock resistance was evaluated in accordance with the
presence of the cracks. A case where no crack generation was
recognized is shown by a "double circle" mark, and a case where the
generation of a very small amount of cracks was recognized is shown
by a "circle" mark. A case where the generation of a large amount
of cracks was recognized is shown by a "cross" mark.
7. Results:
It has been found from Table 2 that it is possible is to obtain the
honeycomb structure capable of bearing the actual use, even in a
case where the bio-soluble fiber, usable without considering any
influence on the health of a human body, is used. In addition, it
has been found from Examples 1, 2 that it is possible to obtain the
honeycomb structure having a characteristic equivalent to that made
with a heretofore used ceramic fiber. Moreover, the honeycomb
structures of Examples 7 to 18 indicated especially satisfactory
results in all of the B-sp test, E-sp test, and E/G test.
INDUSTRIAL APPLICABILITY
In a honeycomb structure according to the present invention, a
plurality of honeycomb segments are securely bonded to one another
without causing any bonding defect such as crack or peel in the
bonded portions of these segments. Therefore, the honeycomb
structure can preferably be used as a catalyst carrier for an
internal combustion engine, a boiler, a chemical reaction device, a
reformer for a fuel cell, and the like in which a catalyst function
is used, or as a filter for trapping fine particles in an exhaust
gas and the like.
* * * * *